AppMockUp - Create the most compelling screenshots for your app.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Placeit - Generate realistic product shots in seconds
Synfig Studio - Just another WordPress site
Smartmockups - Create stunning product mockups, easily and online.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.